The object of the work proposed is to develop an advanced controlled- impedance spring/damping device for an above knee prosthesis which can be controlled by the amputee wearing the limb or, eventually by automatic adjustments to parameters like gait speed and load on the leg. By utilizing recent advances in small robotic actuators and sensors, a practical device is now possible which interfaces with present knee/shin set ups, to implement both automatic and user-controlled variations in the knee impedance for an above knee prosthesis. This will above knee amputees much more direct control over the knee joint. Walking and running may be more smooth and stable and the amputee will be able to adapt easier to variations in cadence and activity, e.g., up hill or down hill walking and sports activities. Such a system (i.e., easily programmable and adjustable) could also function as an evaluation tool during the prosthesis fitting stage, for determining certain pre- programmed settings in a simpler, less expensive knee joint installed in the finished limb.